We propose to recruit pairs of siblings for a molecular genetic search for genes having a role in the development of neovascular age-related macular degeneration (AMD). Two types of sibling pairs will be recruited, extremely discordant sibpairs and extremely concordant sibpairs. Extremely discordant sibpairs will be composed of one member, the index sib, with neovascular AMD, and the second member with few or no aging signs of the macula at the age at which the index sibling developed neovascular AMD. Extremely concordant sibpairs will be composed of two siblings with neovascular AMD. Leukocyte DNA will be purified from blood samples collected from these siblings. The sibpairs will form the basis for a genome-wide linkage study to search for chromosomal regions where the extremely discordant pairs, on average, share fewer alleles than expected by chance alone, and where the extremely concordant sibpairs, on average, share more alleles than expected. Chromosomal regions having these properties are likely to harbor AMD genes. In addition, candidate genes that may have a role in susceptibility to AMD, such as ABCA4 and apoE, will be analyzed by evaluating DNA sequence variations in those genes and looking for a correlation between any alleles and neovascular AMD. To our knowledge, a molecular genetics approach to finding genes for neovascular AMD based on extremely discordant and extremely concordant sibpairs has not been previously carried out by any other group of investigators. If successful, our work should provide substantial progress toward identifying the genetic causes of neovascular AMD, one of the leading causes of legal blindness among the elderly.